In a visible light communications technology, a high-speed bright-and-dark flash signal that is emitted by a fluorescent lamp, a light emitting diode, or the like and that is invisible to naked eyes is used to transmit information, and a wire apparatus of the high-speed Internet is connected to a lighting apparatus and inserted into a power plug to provide plug-and-play. In a system based on this technology, a range reached by an indoor lamplight is covered, and a computer does not need to be connected by using a wire. Therefore, this technology has a broad development prospect.
Compared with a currently used wireless local area network, a visible light communications system can use an indoor lighting device to replace a base station of the wireless local area network to transmit a signal, and a communication speed of the visible light communications system may reach dozens of megabytes to hundreds of megabytes per second, with a future transmission speed possibly exceeding that of fiber optic communications. By using a dedicated computer and mobile information terminal that have a signal sending and receiving function, data such as a high-definition image and animation can be downloaded and uploaded for a long time in any place with an indoor lamplight. This system is also characterized by high security. With a curtain shielding light, information is not leaked outside; moreover, the communication speed is not affected when multiple computers are used at the same time. Because radio wave communication is not used, a department sensitive to an electromagnetic signal such as a hospital may use this system with freedom.
It may be learned based on the foregoing description that, the visible light communications technology can fully utilize lamplight to provide high-rate data transmission together with lighting. Currently, visible light communications that is put into practice is based mainly on a white light LED (Light Emitting Diode, light emitting diode) communications technology. It is estimated that LED will account for more than 50% of global commercial lighting market shares by 2021. Therefore, the visible light communications is no longer limited to laboratories, and is applied to commercial products and enters a rapid growth period, having a broad market prospect.
IEEE (Institute of Electrical & Electronics Engineer, Institute of Electrical and Electronics Engineers) 802.15.7 is a set of visible light communications standards, defines visible light communications content for a physical layer, a MAC (Medium Access Control, Media Access Control) layer, and the like, and provides a standard interface between an LLC (Logical Link Control, logical link control) layer and the MAC layer.
An IEEE 802.15.7 protocol supports bidirectional visible light communications, and enables feedback information to be transmitted by using a reverse visible light link. However, in an actual scenario, although a lamplight for illumination may be used to transmit DL (Downlink, downlink) data to a user, visible light transmission has problems such as high transmit power consumption and low transmission efficiency, and a visible light sending module may be unsuitable for a terminal device such as a mobile phone of a user. As a result, the bidirectional visible light communications is hard to implement, and it is difficult to provide DL data feedback by using an UL (Uplink, uplink) visible light link, which limits application of the visible light communications.